System and method for controlling steering in a rotary steerable system

Abstract

A system and methodology provide control over the directional drilling of a wellbore. A rotational valve is mounted within a drill collar of a rotary steerable system to enable selective actuation of one or more steering pads on the drill collar via an actuating fluid. The rotational valve is controlled via a motor and designed to provide enhanced control over the flow of actuating fluid to the steering pads.

What is claimed is: 
     
       1. A system for drilling a wellbore, comprising:
 a rotary steerable system having:
 a drill collar; 
 a plurality of movable steering pads mounted to the drill collar, the plurality of movable steering pads being hydraulically actuated by a fluid directed through a plurality of ports corresponding with the plurality of movable steering pads; 
 a rotational valve positioned in the drill collar, the rotational valve having a plurality of openings and an additional opening to control flow of the fluid to the plurality of ports for actuating the plurality of movable steering pads, the plurality of openings matching the number of ports; and 
 an electric motor coupled to the rotational valve, the electric motor being controlled to rotate the rotational valve in a manner which controls flow of fluid to desired ports of the plurality of ports, the additional valve opening being located to enable flow through specific ports to specific movable steering pads and the plurality of openings being positioned to enable alignment of the plurality of openings with the plurality of ports to enable simultaneous flow of the fluid to all of the plurality of movable steering pads while the additional valve opening is closed. 
 
 
     
     
       2. The system as recited in  claim 1 , wherein the plurality of movable steering pads comprises three movable steering pads, and the plurality of ports comprises three ports positioned at angular positions 120° apart. 
     
     
       3. The system as recited in  claim 1 , wherein the plurality of movable steering pads comprises four movable steering pads, and the plurality of ports comprises four ports positioned at angular positions 90° apart. 
     
     
       4. The system as recited in  claim 1 , wherein the rotary steerable system further comprises an encoder positioned to measure an angular position of the rotational valve relative to the drill collar. 
     
     
       5. The system as recited in  claim 4 , wherein the rotary steerable system further comprises control electronics, the electric motor and the encoder being coupled to the control electronics. 
     
     
       6. The system as recited in  claim 5 , wherein the electric motor, encoder, and control electronics are located within a pressure housing within the drill collar. 
     
     
       7. The system as recited in  claim 5 , wherein the rotary steerable system further comprises a power source located within the drill collar. 
     
     
       8. The system as recited in  claim 7 , wherein the power source comprises a turbine. 
     
     
       9. The system as recited in  claim 1 , wherein the rotational valve is rotated by the electric motor to direct the fluid through the plurality of ports in a manner which causes individual movable steering pads of the plurality of steering pads to extend while within a desired angular range of rotation of the drill collar. 
     
     
       10. The system as recited in  claim 1 , wherein the rotational valve is rotated by the electric motor to direct the fluid through all of the plurality of ports simultaneously to cause drilling of a straight section of the wellbore. 
     
     
       11. The system as recited in  claim 1 , wherein the rotation of the rotational valve is selectively changed to change the severity of a dogleg being formed during drilling of the wellbore. 
     
     
       12. A method of forming a wellbore, comprising:
 mounting a rotational valve in a drill collar to control flow of an actuating fluid to a plurality of movable steering pads via selective movement of a plurality of openings and an additional opening in the rotational valve into and out of communication with desired ports which rotate with the drill collar during drilling; 
 arranging the plurality of openings to enable alignment of the plurality of openings with the desired ports for simultaneous flow of actuating fluid to all of the plurality of movable steering pads; 
 positioning the additional opening to enable selective flow of the actuating fluid to specific movable steering pads of the plurality of steering pads and to enable closing of the additional opening during the simultaneous flow of actuating fluid to all of the plurality of movable steering pads; and 
 coupling a motor to the rotational valve to rotate the rotational valve in a manner which controls flow of the actuating fluid into the ports via the plurality of openings and the additional opening to enable selective orienting of the drill collar through actuation of the plurality of movable steering pads. 
 
     
     
       13. The system as recited in  claim 12 , further comprising controlling the motor via a micro-controller positioned with the motor at a location within the drill collar. 
     
     
       14. The system as recited in  claim 13 , further comprising employing an encoder to provide data to the micro-controller on the relative angular position of the rotational valve with respect to the drill collar. 
     
     
       15. The system as recited in  claim 14 , further comprising rotating a bit with the drill collar to drill the wellbore. 
     
     
       16. The system as recited in  claim 12 , further comprising forming the rotational valve with three openings angularly spaced to enable simultaneous flow into three corresponding ports for simultaneous actuation of the corresponding, movable steering pads, wherein forming further comprises forming the rotational valve with the additional opening as a fourth opening which may be selectively rotated into cooperation with the three corresponding ports to control a desired directional drilling of a deviated section of the wellbore. 
     
     
       17. The system as recited in  claim 12 , further comprising forming the rotational valve with four openings angularly spaced to enable simultaneous flow into four corresponding ports for simultaneous actuation of the corresponding, movable steering pads, wherein forming further comprises forming the rotational valve with the additional opening as a fifth opening which may be selectively rotated into cooperation with the four corresponding ports to control a desired directional drilling of a deviated section of the wellbore. 
     
     
       18. A method of drilling a wellbore, comprising:
 selectively actuating steering pads on a drill collar of a rotary steerable system via an actuating fluid; 
 controlling flow of the actuating fluid to the actuating steering pads with a motor controlled rotational valve; 
 providing the motor controlled rotational valve with a plurality of openings matching the number of steering pads and an additional opening such that the plurality of openings and the additional opening have a fixed angular displacement with respect to each other; and 
 rotating the motor controlled rotational valve at a plurality of different speeds to provide the desired flow of actuating fluid to the steering pads selectively through the plurality of openings and the additional opening to provide directional control over the rotary steerable system. 
 
     
     
       19. The method as recited in  claim 18 , wherein controlling comprises coupling an electric motor to a rotational valve of the motor controlled rotational valve and to a micro-controller receiving feedback on the angular position of the rotational valve relative to the angular position of the drill collar. 
     
     
       20. The method as recited in  claim 18 , further comprising porting the rotational valve to enable the rotational valve to be rotated in a manner which simultaneously actuates all of the steering pads.